Scallions and a healthy dose of fresh thyme make these grilled sweet potatoes particularly savory.
Heat grill to medium. Peel sweet potatoes, and cut lengthwise into 1/2-inch-thick slices. Toss potatoes in a large bowl with oil, thyme, and cayenne pepper; season with salt and black pepper.
Grill potatoes, turning frequently, until tender when pierced with the tip of a paring knife, 20 to 30 minutes.
Return grilled potatoes to bowl; add butter, and break potatoes into large pieces with the side of a spoon. Toss in scallions, and serve.